calcifying bacteria in extreme ecosystems of the southern Aral Sea region

The processes of microbially induced precipitation of calcium carbonates are widespread in natural environments and are an important part of the biogeochemical carbon cycle. These processes comprised the basis of new "biocementation" technologies, which are extensively developed within the last decade around the world. These technologies are aimed at creating new "self-healing" construction materials, as well as at maintaining the strength of various buildings and building structures. The optimal conditions for the formation of calcites are increased salinity and alkalinity of the environment, which aroused interest in the search for calcifying microorganisms in a variety of ecosystems, including extreme ones. At present, many strains of halophilic and halotolerant bacteria that induce calcination have already been isolated and tested in pilot industrial processes. Most of these bacteria have urease activity, which is the main contributor to the binding of calcium ions to insoluble calcium carbonate. A wide variety of natural ecosystems with optimal conditions for the development of calcifying urobacteria, as well as the economic demand for biocementation technologies, stimulate interest in the search for more and more novel strains of these microorganisms. One of the promising resources to be screened for such organisms is the ecosystem of the drying Aral Sea and the adjacent desert and semi-desert Aral region. Here we present the results of screening various extreme ecosystems of the Aral region for the presence of calcifying microorganisms. We obtained 28 pure cultures of heterotrophic aerobic bacteria from samples of plant residues and soils of the Aral Sea region, 4 of which have urease and calcifying activities, their activities were compared with those of the strains already used to create biocementing preparations. Phylotypes of potential calcifying microorganisms in microbial communities of desert soil, thermal waters, and bottom sediments of a salt lake have been detected by molecular technique, and a description of the phylogenetic diversity of these communities has been given. The obtained results indicated the wide distribution of calcifying microorganisms in the ecosystems of the South Aral region and highlighted the expediency of screening them for new biotechnologically relevant and strains of these organisms.

微生物诱导碳酸钙沉淀（microbially induced calcium carbonate precipitation）过程在自然环境中广泛分布，是生物地球化学碳循环的重要组成部分。这类过程是新型“生物固结（biocementation）”技术的核心基础，近十年来在全球范围内得到了广泛发展。此类技术旨在研发新型“自愈合”建筑材料，同时维持各类建筑及建筑结构的结构强度。
碳酸钙形成的最优条件为环境高盐度与高碱度，这促使研究人员在包括极端生态系统在内的各类生境中开展钙化微生物的筛选工作。目前，诸多可诱导钙化的嗜盐（halophilic）及耐盐（halotolerant）细菌菌株已被分离，并在试点工业流程中完成测试。这类细菌大多具有脲酶活性（urease activity），而脲酶活性是钙离子结合形成不溶性碳酸钙（insoluble calcium carbonate）的主要驱动因素。
多样的天然生境为产脲酶钙化细菌的生长提供了最优条件，加之生物固结技术的市场需求，进一步推动了科研人员对这类微生物新型菌株的挖掘工作。作为这类微生物的潜在筛选资源之一，正在干涸的咸海及其毗邻的荒漠、半荒漠咸海区域生态系统备受关注。
本研究针对咸海区域的各类极端生态系统开展钙化微生物筛查，现将相关结果报道如下：我们从咸海区域的植物残体与土壤样本中分离得到28株异养需氧细菌（heterotrophic aerobic bacteria）纯培养物，其中4株兼具脲酶活性与钙化活性；我们将这4株菌株的活性与现有用于制备生物固结制剂的菌株进行了对比。本研究通过分子生物学技术（molecular technique），在荒漠土壤、热泉（thermal waters）及盐湖（salt lake）底泥（bottom sediments）的微生物群落中检测到潜在钙化微生物的系统型（phylotype），并对这些群落的系统发育多样性（phylogenetic diversity）进行了描述。
本研究结果表明，钙化微生物在南咸海区域（South Aral region）的生态系统中分布广泛，同时证实了针对这类微生物开展新型生物工程相关菌株筛选的可行性与必要性。